In a wireless communication system, such as a long term evolution (LTE) system or a long term evolution advanced (LTE-A) system, an enhanced physical downlink control channel (ePDCCH) is introduced, and channel estimation for the ePDCCH can be performed by using a reference signal sequence.
When using the reference signal sequence to perform the channel estimation for the ePDCCH, the number of the ePDCCHs in a resource block pair may be greater than the number of antenna ports for transmitting the reference signal sequence, causing that in a condition that the number of the antenna ports is limited, the reference signal sequence may not be able to be transmitted through the antenna ports, and thereby the capacity of using the reference signal sequence to perform the channel estimation to the ePDCCH is reduced.